The present invention relates to arc lamps and, more particularly, to a short arc lamp featuring a transparent sealed arc chamber with internal and external integral concave reflecting elements reflecting light from the arc in the same direction.
A short arc lamp generally features basic components of an anode and a cathode separated by a gap, commonly known as an arc gap, which is positioned along the center longitudinal axis of a gas pressurized chamber where a concave, typically, parabolic reflector element is internal or external to the gas pressurized chamber.
During operation, a high voltage is applied across the gap resulting in an electrical arc being produced along the arc gap with simultaneous intense emission of light originating from the excited gas. The emitted light diverges onto, and is collimated by the concave reflector element, and exits through the transparent window of the short arc lamp, thereby providing an intense collimated source of light for a particular. application.
There are basically two configurations for constructing short arc lamps:
The first configuration includes teachings of U.S. Pat. Nos. 4,633,128, 5,561,338, 5,418,420, and 5,399,931, to Roberts et al., of U.S. Pat. Nos. 4,940,922, and 4,724,352 to Schuda et al., and of U.S. Pat. No. 5,869,920 to Kavanagh.
In each of these short arc lamp teachings, the arc chamber (which confines a vacuum tight volume by an integral parabolic reflector surface and a transparent window), is constructed from a hollowed out portion of opaque solid material, typically, solid ceramic material, in order to withstand gas pressures of more than several atmospheres.
A common limitation of short arc lamps in general is their high sensitivity to the locus and shape of the light source, because of the short focal length of their reflector.
This is so unless short arc lamps having large reflectors are employed, however the construction of large arc chambers which are needed in this configuration to accommodate large reflectors is costly and technologically difficult to implement, thus a second configuration is used; that of short arc lamps featuring an arc chamber confined within a transparent envelope made of glass or quartz at relatively high gas pressures and which have an external reflector.
Such short arc lamps are described in U.S. Pat. No. 5,369,557, issued to Ronney and in U.S. Pat. No. 4,734,829, issued to Wu et al.
In each of these teachings, in which the reflecting surfaces of light are positioned only external to the arc chamber envelope, the transparent envelope has the advantage of an efficient transmission of light to the external reflector.
Yet a portion of the radiation of the discharge, in the backward direction, is prevented from reaching the external reflector by the parts of the discharge chamber itself and therefore radiation losses occur.
Thus, it seems beneficial to have a novel third configuration of a short arc lamp which will substantially resemble the second configuration, but which avoids its limitation. I.e., it would be useful to have a short arc lamp featuring a transparent sealed arc chamber, which does not suffer from the aforementioned radiation losses.
In addition, a common feature to the short arc lamps of both first and second configurations which were described above is that the light wavelength spectrum along the beam cross section is usually uniform. An exception to this is a beam of light with different colors which was formed by an arc lamp which incorporated two different light sources as described e.g. in U.S. Pat. No. 5,655,832 to Pelka, et al.
Still, there does not exist nowadays a short arc lamp in which the radiation which is being emitted from a single arcing chamber is split to form a beam of light having a profile of two concentric regions in which the inner region has one waveband, e.g. in the infrared and the outer region has a second wavelength band, e.g. in the vis/uv.
The present invention fulfills this gap and provides other related advantages.